Pain is a result of many medical conditions and procedures, and is the most common reason for physician visits in the United States. Pain can be acute, lasting until the source is removed or underlying condition heals, or it can be chronic, persisting for years. Acute pain can be caused by injury, stimulus of the nervous system, surgery, child birth, or “break-through pain” of a pain management regimen. Chronic pain can be caused by conditions such as cancer, arthritis, neuropathy, and can be idiopathic or psychogenic.
Opioids are a broad class of pharmaceuticals used clinically primarily for the treatment of pain. They are amongst the oldest known pharmaceuticals, and use of the opium poppy predates written history. The class includes morphine, codeine, hydrocodone, hydromorphone, oxycodone, tapentadol, naltrexone, fentanyl, sufentanyl and numerous others.
Hydrocodone is a semi-synthetic opioid derived from codeine and thebaine. It is commercially available in the United States as an oral tablet, capsule, suspension, syrup, or solution. Every hydrocodone product currently approved in the United States is in combination with another active ingredient. Products indicated for pain relief are combined with another analgesic such as acetaminophen, or less commonly ibuprofen, both of which can cause liver toxicity and are contraindicated in patients with hepatic impairment. The lack of a hydrocodone formulation without an additional active ingredient, and the lack of extended release hydrocodone formulations indicated for pain, limits the ability of physicians to treat pain in patients with hepatic impairment.
Opioids can be formulated in extended release formats to reduce dosing frequency and achieve more constant plasma levels. They are generally indicated for the continuous management of moderate to severe pain. Hydrocodone in combination with chlorpheniramine is available in a polistirex extended release capsule (Tussicaps®, Hi-Tech Pharma Co, also available as an oral suspension from Tris Pharma and UCB incorporated) as a remedy for cold, flu, allergies, and other breathing illnesses, although there does not currently exist an approved hydrocodone extended release product indicated for pain.
Oxycodone hydrochloride is available as an extended release tablet (Oxycontin®, Purdue Pharma LP). Tapentadol hydrochloride is available as an extended release tablet (Nucynta® ER, Janssen Pharmaceuticals). Oxymorphone hydrochloride is available as an extended release tablet (Opana® ER, Endo Pharmaceuticals, also available from Actavis and Impax Labs). Morphine sulfate is available as extended release capsules (Avinza®, King Pharmaceuticals, Kadian®, Actavis, also available from Watson Labs), extended release capsules in combination with naltrexone (Embeda®, King Pharmaceuticals) and extended release tablets (MS Contin, Purdue Pharma, Oramorph®, Xanodyne Pharmaceuticals, also available from Nesher Pharmaceuticals and Rhodes Pharmaceuticals). Hydromorphone hydrochloride is available as an extended release tablet (Exalgo®, Mallinkrodt). Hydromorphone hydrochloride extended release tablets (Palladone®, Purdue Pharma) were approved by the FDA in September of 2004 for continuous management of persistent, moderate to severe pain, but were taken off the market in July of 2005 due to serious and potentially fatal adverse reactions when taken with alcohol.
Hepatic impairment is a condition wherein normal functioning of the liver is reduced. Hepatic impairment can be acute, with rapid onset, or chronic. Chronic hepatic impairment, or cirrhosis, can occur from many causes, such as excessive consumption of alcohol, hepatitis, autoimmune disease, heredity, or metabolism, or can be idiopathic. Liver damage is generally irreversible, and treatment consists of prevention of progression and treatment of symptoms. In severe cases, liver transplant is the only option. Hepatic impairment can exhibit no significant symptoms, or may be characterized by such symptoms as reduced ability for the blood to clot (coagulopathy) and brain dysfunction (encephalopathy), fluid retention in the abdominal cavity, increased infection risk, hypogonadism, change in liver size, jaundice, and increased sensitivity to medication.
It is a problem that opioids, including extended release opioids, generally require reduced dosing in patients with hepatic impairment, because the liver is the source of most opioid metabolism. Using the same dosage in hepatically impaired patients as in those without hepatic impairment in general leads to higher Cmax, higher AUCs, longer t1/2, and can result in excessive or persistent sedation, coma or death. In a recent review (Johnson, S J. Opioid Safety in Patients with Renal or Hepatic Dysfunction, Pain Treatment Topics, June 2007), it was recommended that codeine, methadone, meperidine, and propoxyphene not be used in patients with severe hepatic impairment. For hydromorphone and hydrocodone, the recommendation was to start with 50% of the usual dose, oxycodone ⅓ to ½ of the usual dose, and for morphine, the recommendation was to increase the dosing interval by twice the usual time period. In another recent article, (Bond, M., Effects of renal impairment and hepatic impairment on the pharmacokinetics of hydrocodone after administration of a novel extended-release hydrocodone tablet formulated with OraGuard™ technology, Pain Week Accepted Abstracts, 2013), it was found that the delivery of extended release hydrocodone without an immediate release component led to systemic exposure to hydrocodone that was ˜70% higher in subjects with moderate hepatic impairment vs normal hepatic function. Mean hydrocodone AUC was 269 ng*hr/mL in subjects with moderate hepatic impairment, vs. 155 ng*hr/mL in subjects with normal hepatic function.
Similarly, opioid dosing of patients with hepatic impairment can lead to increases or decreases in the plasma levels, durations, and AUCs of metabolites.
Even mild and moderate hepatic impairment can lead to modified dosing requirements of opioids. FIG. 1 shows the measured increase Cmax and AUC of four approved extended release opioid products in mild and moderate hepatic impairment relative to subjects with no hepatic impairment, extracted from package inserts.
Extended release oxycodone (Oxycontin®, Purdue Pharma LP) was shown to have a Cmax increase of 1.5-fold compared to subjects without hepatic impairment, and an increase in AUC of 1.95-fold. The package insert has the following instruction: “A study of OxyContin in patients with hepatic impairment demonstrated greater plasma concentrations than those seen at equivalent doses in persons with normal hepatic function. Therefore, in the setting of hepatic impairment, start dosing patients at ⅓ to ½ the usual starting dose followed by careful dose titration. Data from a study involving 24 patients with mild to moderate hepatic dysfunction show peak plasma oxycodone and noroxycodone concentrations 50% and 20% higher, respectively, than healthy subjects. AUC values are 95% and 65% higher, respectively. Oxymorphone peak plasma concentrations and AUC values are lower by 30% and 40%. These differences are accompanied by increases in some, but not other, drug effects. The mean elimination t for oxycodone increased by 2.3 hours.”
Extended release tapentadol tablet (Nucynta® ER, Janssen Pharmaceuticals) was demonstrated to have an increase of 1.4-fold in Cmax and an increase of 1.7-fold in AUC for subjects with mild hepatic impairment, and an increase of 2.5- and 4.2-fold in Cmax and AUC respectively for those with moderate hepatic impairment. The package insert contained the following information: “NUCYNTA® ER has not been studied in patients with severe hepatic impairment. The use of NUCYNTA® ER in this population is not recommended. Use NUCYNTA® ER with caution in patients with moderate hepatic impairment. Initiate treatment in these patients using 50 mg NUCYNTA® ER and administer no more frequently than once every 24 hours. The maximum recommended dose for patients with moderate hepatic impairment is 100 mg of NUCYNTA® ER once daily. Administration of tapentadol resulted in higher exposures and serum levels to tapentadol in subjects with impaired hepatic function compared to subjects with normal hepatic function. The ratio of tapentadol pharmacokinetic parameters for the mild and moderate hepatic impairment groups in comparison to the normal hepatic function group were 1.7 and 4.2, respectively, for AUC; 1.4 and 2.5, respectively, for Cmax; and 1.2 and 1.4, respectively, for t1/2. The rate of formation of tapentadol-O-glucuronide was lower in subjects with increased liver impairment.”
Extended release oxymorphone (Opana® ER, Endo Pharmaceuticals) was shown to have an increase in AUC of 1.6-fold and 3.7-fold in subjects with mild and moderate hepatic impairment, respectively, compared to subjects without hepatic impairment. The package insert contains the following: “The liver plays an important role in the pre-systemic clearance of orally administered oxymorphone. Accordingly, the bioavailability of orally administered oxymorphone may be markedly increased in patients with moderate to severe liver disease. The disposition of oxymorphone was compared in 6 patients with mild, 5 patients with moderate, and one patient with severe hepatic impairment and 12 subjects with normal hepatic function. The bioavailability of oxymorphone was increased by 1.6-fold in patients with mild hepatic impairment and by 3.7-fold in patients with moderate hepatic impairment. In one patient with severe hepatic impairment, the bioavailability was increased by 12.2-fold. The half-life of oxymorphone was not significantly affected by hepatic impairment . . . . Use OPANA ER with caution in patients with mild impairment, starting with the lowest dose and titrating slowly while carefully monitoring for side effects.”
Extended release hydromorphone (Exalgo®, Mallinkrodt) demonstrated an approximately 4-fold increase in both Cmax and AUC in subjects with moderate hepatic impairment compared to subjects without hepatic impairment. The package insert contains the language “Start patients with moderate and severe hepatic . . . impairment on a reduced dose and closely monitor during dose titration. The pharmacokinetics of hydromorphone in severe hepatic impairment patients have not been studied. Further increase in Cmax and AUC0-∝ of hydromorphone in this group is expected, therefore, use an even more conservative starting dose.”
Extended release morphine sulfate (Kadian®, Actavis) has the following information in its package insert: “Hepatic Failure: The pharmacokinetics of morphine were found to be significantly altered in individuals with alcoholic cirrhosis. The clearance was found to decrease with a corresponding increase in half-life. The M3G and M6G to morphine plasma AUC ratios also decreased in these patients indicating a decrease in metabolic activity . . . the increased risks associated with its use in the following populations should be considered: . . . those with severe impairment of hepatic . . . function. KADIAN® should be administered with caution, and in reduced dosages in . . . patients with severe . . . hepatic insufficiency.”
The changes in pharmacokinetic parameters such as AUC, Cmax, t1/2 of a drug and/or its metabolites in patients with hepatic impairment can lead to many problems, including need for adjusting dose, complications for physicians in prescribing, need for liver function tests, lack of availability of correct doses, lack of availability of certain medications to those with hepatic impairment, and overdosing.